The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Diesel engine operation involves combustion that generates exhaust gas. During combustion, an air/fuel mixture is delivered through an intake manifold to cylinders and is combusted therein. After combustion, the pistons inside the cylinders force exhaust gas in the cylinders into an exhaust system.
The exhaust system may include a selective catalyst reduction (SCR) unit that reduces NOx emission before the exhaust gas is released to the atmosphere. A dosing system injects a reductant (such as, for example only, urea) into the exhaust gas upstream from the SCR unit.
To effectively reduce NOx emissions in the SCR unit, monitoring the concentration of NOx in the exhaust gas upstream from the SCR unit ensures effective reduction of NOx emissions. For example, an exemplary exhaust system generally includes a first NOx sensor upstream from the SCR unit and a second NOx sensor arranged downstream from the SCR unit. The first NOx sensor measures the amount of NOx in the exhaust gas prior to treatment. The dosing system injects a predetermined amount of reductant based on the measured NOx emissions. The second NOx sensor monitors NOx emissions released to the atmosphere. NOx sensors are costly and the readings from the NOx sensors also need to be monitored for accuracy.